1. Field of the Invention
This invention relates to a motor oil composition for internal combustion engines. More particularly, this invention relates to a blend of three solvent-extracted neutral (SEN) oils as a base oil used in a multi-grade heavy duty motor oil. In one aspect, this invention forms the basis of an SAE 10W-30 grade CD/SF oil that meets specifications for lubrication of both turbocharged diesel and gasoline engines.
2. Discussion of the Art
Lubricating oils must provide minimal frictional wear in an engine over a wide range of operating temperatures. These engine temperatures can range from below freezing during cold weather starting to above 400.degree. F. (200.degree. C.) during severe usage.
A continuing problem in the art is formulating a multi-grade oil which will maintain all of the desired characteristics, i.e. low viscosity at cold starting temperatures and high viscosity to decrease consumption at operating engine temperatures, without sacrificing or compromising any of these features. These qualities are critical for satisfactory performance under severe conditions, such as in turbocharged diesel engines used to power large trucks and construction equipment.
Merely blending a base oil that meets the viscometric requirements of a multi-grade oil does not mean that the oil will survive the severe environment of turbocharged diesel engine lubrication over an extended period. The oil must also meet the requirements of engine tests used to qualify for various SAE ratings and commercial marketing. A blend of various base oils and additives is usually necessary to provide both low temperature cranking properties and thermal stability at higher temperatures.
The results of engine tests are usually not predictable from the viscometric data of the base oil. The addition of significant amounts of synthetic additives can alter the delicate balance of the base oil blend, with the result that the base oil blend itself must be adjusted to compensate for the viscosity characteristics of the additives. Occasionally this problem is so pronounced that incorporating additives to correct one defect, such as poor oil consumption, can result in another defect, such as a failure to meet viscosity requirements. A common objective is to formulate a base oil blend with minimal dependence on additive chemistry.
It is generally accepted that 10W-30 engine oils will provide advantages in cold starting and fuel savings over 15W-40 engine oils. However, wear control and consumption problems often arise because of the limitations of the base oil. 10W-30 oils have previously required relatively large amounts of costly lubricant additives and viscosity index improvers to correct such deficiencies. It is therefore unusual to find a base oil blend that allows a 10W-30 oil to approach the performance standards of a 15W-40 oil.
Lubricants are often blended to meet the specific requirements of a limited type of engine and a certain range of operating conditions. For example, an oil designed for heavy duty diesel engines would not be expected to give good performance on gasoline engines. It is unique that a 10W-30 oil can pass heavy duty diesel engine tests. It is of special significance that this same oil can achieve an SF rating for gasoline engines.